The present invention relates generally to satellite-based landing navigation systems, and more particularly, relates to a portable tester designed to verify the operational status of a ground facility of the satellite-based landing navigation system.
Pilots typically use landing navigation systems when they are landing an aircraft. These systems assist the pilot in maintaining the aircraft along a predetermined glidepath associated with a particular landing strip or runway. In general, ground-based navigation systems are employed. Two common ground-based navigation systems currently in use are the Instrument Landing System (ILS) and the Microwave Landing System (MLS).
Due to limitations in the ILS and MLS Systems, including cost and single approach limitations, the Federal Aviation Administration (FAA) is currently transitioning the National Airspace System (NAS) from ground-based navigation systems to satellite-based navigation systems. In this endeavor, the FAA, with assistance from industry, is developing a Local Area Augmentation System (LAAS) to provide a satellite-based landing solution designed to assist pilots during approach and landing of an aircraft.
The LAAS uses a differential global positioning system (DGPS). The DGPS includes a global positioning system (GPS) and at least one ground station. The GPS uses a number of orbiting satellites and a receiver on an aircraft to determine the position of the aircraft with respect to ground. With the satellite information, the receiver can determine the position, speed, and altitude of the aircraft. By adding a ground station, the DGPS can correct errors that may occur in the transmission of data from the satellites to the receiver. As a result, the DGPS can determine the position of the aircraft with a high degree of accuracy.
In 1998, the FAA initiated a program to develop requirements for developing and deploying a LAAS Ground Facility (LGF). The LGF will monitor the satellite constellation, provide LAAS corrections and integrity data, and interface with air traffic control. As a result of this program, the FAA released Specification FAA-E-2937A for a Category I LGF on Apr. 17, 2002, the contents of which are incorporated by reference. This specification establishes the performance requirements for the LGF.
After the LAAS is installed at an airport, the system needs to be certified as operational before pilots can rely on the LAAS to provide approach and landing guidance. Test flights are required to certify the system. During the test flights, test pilots land aircraft that are not currently being operated for commercial purposes (e.g., transporting goods and/or people) using the LAAS. The LAAS data from the test flights is compared to data from an FAA approved truth system to ensure that the test pilot received accurate glidepath information.
These test flights are very expensive and can be dangerous if the pilot receives erroneous information. If the test flight indicates problems with the LAAS, additional test flights will be required. Therefore, it would be desirable to have a portable tester that can verify LGF operability prior to performing a test flight. Once the LAAS has been certified and is operational at an airport, it is also desirable to have a portable tester to perform routine maintenance tests on the LGF.
A portable tester for testing a satellite-based navigation system ground facility is provided. In a preferred embodiment the portable tester includes a receiver and a computer. The receiver is operable to receive both Global Positioning System (GPS) signals from a plurality of satellites and Very High Frequency (VHF) broadcasts from a ground facility. The computer is operable to tune the receiver and select a glidepath for a particular runway. The computer can then determine whether the ground facility is operational by comparing the GPS signals and VHF broadcasts obtained by the receiver with expected results.